Sealing unit for sealing gusset bottom bags

ABSTRACT

A sealing unit for sealing together face-to-face strips of flexible material joined along their bottoms by a fold which is tucked upwardly to form a gusset of W-shaped cross section along the fold, the strips being advanced lengthwise and in upright planes along a predetermined path. The sealing unit comprises a primary rectangular seal bar and, spaced downstream therefrom, a gusset seal bar and a secondary rectangular seal bar, the seal bars being operable to seal the strips in such a manner as to form a series of gusset bottom bags. To enable the sealing of strips of various heights with only minor changes in the sealing unit, the primary rectangular seal bar seals the strips through a protective curtain which covers the strips except for the gusset and which allows the primary rectangular seal bar to extend downwardly alongside the gusset without pressably engaging the latter while sealing crosswise of the remainder of the strips. In order to enable the sealing of strips of various thicknesses, the gusset seal bar is mounted for adjustment laterally of the strips and relative to the secondary rectangular seal bar.

United States Patent 1 3,620,884

[ 72] inventor Donald T. Peterson Primary Examiner-Benjamin A. BorcheltRockford, Ill. Assistant Examiner-James M. Hanley [21] Appl. No. 886,980Attorney-Wolfe, Hubbard, Leydig, Voit and Osann, Ltd.

[22] Filed Dec. 22, 1969 [45] Patented Nov. 16, 1971 [73] AssigneeRiegel Paper Corporation ABSTRACT: A sealing unit for sealing togetherface-to-face New York strips of flexible material joined along theirbottoms by a fold which is tucked upwardly to form a gusset of W-shapedcross [54] SEALING UNIT FOR SEALING GUSSET BOTTOM section along thefold, the strips being advanced lengthwise and in upright planes along apredetermined path. The sealln BAGS g 4Chims9Dmwing Figs unit comprisesa primary rectangular seal bar and, spaced downstream therefrom, agusset seal bar and a secondary [52] US. 156/553 rectangular seal bar,the seal bars being operable to seal the 156/251 156/515 strips in sucha manner as to form a series of gusset bottom [51] Int. Cl bags Toenable the ealing of strips of various heights 1332b 31/08 only minorchanges in the sealing unit, the primary rectangu- [50] Field ofSearch156/251, |ar seal bar seals the Strips through a protective curtainwhich 515, 583, 93/DIG 1 covers the strips except for the gusset andwhich allows the primary rectangular seal bar to extend downwardlyalongside [56] References Cited the gusset without prcssably engagingthe latter while sealing UN T STATES PATENT 5 crosswise of the remainderof the strips. In order to enable the 3,531,359 9/l970 Jones et al.156/515 sealing of strips of various thicknesses, the gusset seal bar is3,395,622 8/1968 Kugler 93/35 mounted for adjustment laterally of thestrips and relative to 3,047,05l 7/1962 Matveeff 156/539 the secondaryrectangular seal bar.

.-I ll I 4/ i 5 5 a I =--f= ll 1/ 1% 5 5 E T l 17 g 1/ i l" :2

PATENTEDuuv 1s nan SHEET 1 OF 2 SEALING UNIT FOR SEALING GUSSETBO'I'I'OM BAGS BACKGROUND OF THE INVENTION This invention relates to asealing unit for sealing together face-to-face strips of flexiblematerial joined by a fold which is tucked inwardly to form a gusset ofW-shaped cross section along the fold. The strips are advanced along apredetermined path, and the sealing unit is operable to seal the stripscrosswise at spaced intervals to form a series of connected gussetbottom bags. The sealing unit seals the strips with a generallyrectangular seal tenninating at the gusset and with a generallytriangular seal located on the gusset.

SUMMARY OF THE INVENTION The primary aim of the present invention is toprovide a new and improved sealing unit for convening strips into gussetbottom bags and capable of sealing strips which may vary in height fromrun-to-run while requiring fewer and less expensive changes between runsthan prior sealing units of the same general character.

A more detailed object is to achieve the foregoing by providing a uniquesealing unit having a first sealing bar for forming at least the majorpart of each rectangular seal and having a second sealing bar spacedalong the path of the strips from the first and operable to form thetriangular seals on the gussets of the strips.

A further object is to take advantage of a protective curtain, whichkeeps the rectangular sealing bar from sticking to the strips, for alsomaking only a selected length of such bar effective to seal the stripsso that the same bar can be used to seal strips of various heights.

Another important object of the invention is to provide a sealing unitwhich, as compared with prior devices of the same general type, requiresfewer and simpler modifications between runs in order to seal strips ofdifferent thicknesses. This is accomplished by mounting the second orgusset sealing bar for adjustment laterally of the strips and relativeto the rectangular sealing bar.

The invention also resides in the novel provision of a secondaryrectangular sealing bar which is associated with the gusset sealing barto insure that the strips will be sealed in the area between thetriangular seal and the seal formed by the primary rectangular seal bar,the adjustability of the gusset sealing bar enabling efiective sealingby the secondary bar regardless of the thickness of the strips.

Other objects and advantages of the invention will become apparent fromthe following detailed description when taken in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary perspectiveview of a partially open gusset bottom bag. v

FIG. 2 is a fragmentary front elevation of the bag of FIG. 1 but showingthe bag unopened.

FIG. 3 is an enlarged, fragmentary cross section taken substantiallyalong the line 3-3 of FIG. 2 and showing the bag slightly open.

FIG. 4 is a fragmentary elevation of a sealing unit embodying the novelfeatures of the present invention.

FIG. 5 is an enlarged, fragmentary cross section taken substantiallyalong the line 5-5 of FIG. 4.

FIG. 6 is an enlarged cross section taken substantially along the line6-6 of FIG. 4.

FIG. 7 is a perspective view of a portion of a backing mechanism shownin FIG. 6.

FIG. 8 is a perspective view of the gusset seal bar, secondary seal bar,and a support member.

FIG. 9 is a fragmentary cross section taken substantially along the line99 of FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in thedrawings for purposes of illustration, the invention is embodied in apackaging machine having a heat sealing unit 10 (FIG. 4) for sealingtogether face-to-face strips 11 of flexible material to form gussetbottomed bags 12 (one bag being shown in FIG. I). The completed bagcomprises front and back panels 13 (FIG. 3) joined together along themajor length of their side edges by a narrow rectangular side seal 14(FIG. 2). Along their bottoms, the panels 13 are joined by a bellowslikefold which is formed by two outer folds 15 (FIG. 3) and an intermediateand inwardly tucked reverse fold 16, thus resulting in the formation atthe bottom of the bag of a gusset 17 of W-shaped cross section. Thegusset extends along the lower edge portions of the side panels (and thestrips 11 from which the panels are formed) with each adjacent pair oflegs of the W constituting a double-walled flap 18.

The inner and outer walls 19 and 20 at each end of each flap 18 arejoined together by a seal 21 (FIG. 2) which extends over a generallytriangular area including the flap comer and which terminates at aninner edge 22. The latter starts at the intersection 23 of the inner orupper end of the fold I6 and the inner edge of the side seal 14 andextends diagonally downwardly at an angle of about 45 degrees to thelower flap edge or fold 15.

When the bag 12 is opened, the \V-shaped gusset I7 is flattened out byunfolding of the flaps I8 so that the inner walls 19 of the two flapslie substantially in the same horizontal plane to form a generally flatand rectangular bottom wall 24 as shown in FIG. I, the outer walls 20 ofthe flaps becoming part of the upright front and rear sides of the bag.Due to the triangular shape of the seals 21, the joined end portions ofthe flaps 18 ultimately turn up about a fold line 25 as the bag isopened, and the unsealed triangular portions 26 of the flaps between theseals are bent upwardly and become part of the end walls of the bag.Reference may be had to Morgan US. Pat. No. 2,821,337 for a moredetailed description of a bag similar to the bag 12.

To make the bags 12, the packaging machine includes a plow (not shown)which folds or doubles an initially horizontal web of flexible materialalong its longitudinal center to form the face-to-face strips 11, themachine advancing the strips step-by-step and in upright positions alonga predetermined path. During such advance, the lower fold connecting thestrips is tucked upwardly between the strips to form the W- shapedgusset 17 along the lower margins of the strips. After the gusset hadbeen formed, the sealing unit 10 seals the strips together atlongitudinally spaced intervals, the sealing being effected as thestrips dwell between successive steps. As the strips advance past thesealing unit, their upper margins straddle and slide along a stationarysplitter bar 28 (FIG. 4) which is disposed above the strips to keep theextreme upper margins of the strips spread apart and thus enable easyopening of the bags at stations downstream of the sealing unit.

As shown most clearly in FIG. 4, the sealing unit I0 is operable to sealthe strips 11 together with a generally rectangular seal 29 and with agenerally triangular seal 30, the latter seal being formed on the gusset17 or lower margins of the strips. The rectangular seal 29 extendsupwardly along the strips from the top of the triangular gusset seal 30to an elevation which is level with the lower edge of the splitter bar28. For brevity, the portions of the strips which extend from the top ofthe gusset seals 30 upwardly and which are sealed by the rectangularseals 29 will hereinafter be referred to as panels" 31 since theseportions correspond generally to the panels I3 of the ultimate bags I2.

After the strips 11 are sealed and advanced beyond the sealing unit 10,a knife (not shown) cuts the strips along the vertical centerlines ofthe seals 29 to separate the strips into individual bags 12. Being thuscut, each rectangular seal 29 forms the adjacent side seals I4 ofadjacent bags, and each triangular gusset scal 30 forms the adjacentseals 21 on the gussets of adjacent bags.

In many instances, the same packaging machine may be used to makevarious lengths or heights of bags 12. That is, the machine may be usedto run a series of bags of l height for a period of time and thenchanged over to run longer or shorter bags. This is accomplished byloading the machine with a wider or narrower web of bag material suchthat, when the web is folded, the resulting strips 1 1 are longer orshorter (in a vertical sense) than those fonned during a previous runwith a web of a given intermediate width. With some machines capable ofmaking bags of various heights, a so-called constant top datum lineconcept is employed wherein the upper edges of all strips, regardless oftheir height, proceed along the same horizontal top datum line duringadvancement of the strips. The vertical position of the splitter bar 28thus need not be adjusted when the machine is changed over. When thisconcept is used, however, the bottom edges of the strips of 1 heightwill advance along a different lower horizontal line that the bottomedges of strips of a different height.

Other packaging machines rely upon a so-called constant bottom datumline concept. Thus, the lower edges of strips 11 of all heights advancealong the same horizontal bottom datum line but, when the machine ischanged over to run bags of a different height, the upper edges of thestrips proceed along a different top horizontal line that the upperedges of the strips of the preceding run. In this case, the elevation ofthe splitter bar 28 must be changed when the packaging machine is set upto run bags 12 of a new height.

Regardless of which datum line concept is employed, certain changes mustbe made to the sealing unit lwhen the packaging machine is changed overto run bags 12 which differ in height from those of a preceding run. inother words, if the common top datum line concept is followed, theelevation of the gusset seals 30 on one run of bags will be difi'erentthan the elevation of the gusset seals on the bags of the next run. Thesealing unit thus must be modified to accommodate the differentelevation of the gusset seals. Similarly, if the common bottom datumline concept is employed, the changing of the elevation of the splitterbar 28 makes necessary certain modifications in the sealing unit.

In accordance with the primary aspect of the present invention, thesealing unit is made up by a first sealing mechanism 33 for forming atleast the major length of the rectangular seals 29, and by a secondsealing mechanism 34, spaced along the bag path from the first, forforming the gusset seals 30. The use of separate sealing mechanisms forforming the two types of seals simplifies the changes needed to be madeto the sealing unit when the packaging machine is changed over to formbags 12 of a different height and, in addition, all of the more complexand expensive parts of the sealing unit can be used regardless of theheight of the bags being run and none need be replaced with parts of adifferent size when the machine is changed over.

Herein, the first or primary sealing mechanism 33 (FIGS. 4 and 9) forforming the major length of the rectangular seals 29 is located upstreamof the second or gusset sealing mechanism 34 and comprises a front,vertically extending sealing bar 35 and a rear, vertically extendingbacking bar 36, the two bars being disposed directly across from oneanother on opposite side of the strips 11. Each bar is equal in width tothe width of the rectangular seal 29 and is of a height which is equalto or greater than the height of the panels 31 of the tallest stripswhich the packaging machine will handle. The bars are carried on theupper end portions of swingable arms 37 and are mounted for verticaladjustment on the arms by means of bolts 38 which extend throughvertically elongated slots 39 formed in the upper end portions of thearms.

Formation of each rectangular seal 29 is effected by swinging thesealing and backing bars 35 and 36 toward one another in unison (byswinging the arms 37) while the strips 11 are dwelling and by pressingthe strips between the bars and simultaneously heating the strips withthe bars. The inside faces only of the strips are coated with athermoplastic material which, when heated and pressed by the bars,serves to seal the strips together in the areas located between thebars. Heat is applied to the bars by electric heaters 40 (FIG. 9) whichare embedded in the upper end portions of the arms, the heat beingconducted to the bars through the arms.

To prevent the hot sealing and backing bars 35 and 36 from sticking tothe outer faces of the strips 11, a protective curtain 41 (FIGS. 4 and9) of slick, heat conductive material is draped over the splitter bar 28adjacent the tow bars and straddles the strips in such a position that,during sealing, one panel of the curtain is sandwiched between thesealing bar and the front strip while the other panel of the curtain issandwiched between the backing bar and the rear strip. Preferably, thecurtain is made of fibrous material impregnated with Teflon and conductsthe heat of the bars to the strips. Thus, the strips are sealed by thebars through the curtain, the latter preventing direct contact of thebars with the strips to eliminate any danger of the bars sticking to thestrips.

ln carrying out the invention, the curtain 41 is employed to advantageto enable the use of the same sealing and backing bars 35 and 36regardless of the height of the strips 11 and to avoid the need of usingbars of a different length each time the packaging machine is changedover to run strips of a different height. For the most part, these endsare achieved by using the curtain to make only a desired portion of thetotal length of each bar effective to actually seal the strips.

The foregoing may be best explained by first referring to FIGS. 5 and 9wherein it will be seen that the panels 31 of the strips 11 are equal inthickness to the thickness of two individual strips while the gusset 17is equal in thickness to thickness of four individual strips, this beingdue to the folded material in the gusset. Now, the bars 35 and 36 mustnot be permitted to press against the relatively thick gusset to anyappreciable degree because, if this occurred, the gusset would eitherprevent inward movement of the bars to the extent necessary to seal thepanels (which are of lesser thickness than the gusset) or would causethe bars to approach the panels at an angle, thus resulting innonuniform sealing along the height of the panels. Also, regardless ofthe height of the strips and the elevation of the splitter 28, the upperends of the bars always must be positioned just below, and must notextend above, the lower edge of the splitter so that the bars will befree to move inwardly to press the panels together without the inwardmovement of the bars being limited or influenced by the splitter.

The curtain 41 is employed to enable these criteria to be maintainedwhile permitting the use of the same bars 35 and 36 regardless of theheight of the strips 11. For purposes of explanation, let it be assumedthat the strips shown in FIG. 9 are the shortest which will be handledby the packaging machine. Now, the bars, being at least as long as theheight of the panels 31 of the tallest strips handled by the machine,are positioned with their upper ends below the lower edge of thesplitter 28 and thus their lower end portions extend downwardlyalongside the gusset 17. To keep the lower end portions of the bars fromengaging the gusset and preventing the upper end portions fromeffectually sealing the panels 31, the curtain 41 is draped over thesplitter in such a manner that the lower edges of the curtain panelsterminate at or just short of the upper margin of the gusset.

Each panel of the curtain 41 is at least equal in thickness to thethickness of one individual strip 11. Accordingly, when positioned asshown in FIG. 9, the curtain panels keep the lower end portions of thebars 35 and 36 from pressing against the gusset 17 but still transmit tothe strip panels 31 the heat and pressure of the upper end portions ofthe bars so that the panels 31 are sealed together to form therectangular seals 29. Thus, even though the bars are considerably longerthan the panels 31, the curtain causes the bars to seal only the panels31 and enables such sealing to be effected uniformly since, with thecurtain in position, all of the material engaged by the face of each barlies in a common upright plane.

it the common top datum line concept is employed and the packagingmachine changed over to run strips ll having a greater height than thoseshown in FlG. 9, it is necessary only to change the curtain 41 in such amanner that the lower edges of the curtain panels terminate at the uppermargin of the gusset 17 of the taller strips, the gusset of such stripsbeing disposed at a lower elevation that the gusset of the shorterstrips of the preceding run. Most desirably, the curtain is simplyreplaced with one having longer panels capable of extending downwardlyto the gusset of the taller strips. No further changes to the sealingmechanism 33 are necessary.

If the packaging machine employs the common bottom datum line conceptand is changed over to run strips 11 of greater height than those shownin FIG. 9, the elevation of the splitter 28 is adjusted to correspond tothe elevation of the upper edges of the taller strips and, in addition,the elevation of the bars 35 and 36 is changed (by loosening the bolts38) so as to position the upper ends of the bars just below the loweredge of the splitter. Also, the curtain 41 is replaced with one havingpanel corresponding generally in length to the panels 31 of the tallerstrips.

Accordingly, regardless of which datum line concept is used, only therelatively inexpensive curtain 41 of the sealing mechanism 33 need bereplaced when the packaging machine is changed over to form bags 12 of adifferent height. At most, the bars 35 and 36 need only be adjusted andneed not be replaced with bars of a difierent length.

The gusset sealing mechanism 34, which is located downstream from thesealing and backing bars 35 and 36 as shown in FIG. 4, comprises a frontgusset seal bar 45 (FIG. 5) and a rear gusset backing bar 46 (FIG. 7),the two bars being disposed directly across from one another on oppositesides of the strips 11. Each bar is formed in the shape of a truncatedtriangle the size of the gusset seal 30. The bars are mounted on frontand back support blocks 47 and 48 which arecarr ied on; the upper endportions of paired swingable rods 49 and 50, respectively.

Formation of each gusset seal 30 is effected by swinging the gussetsealing bar 45 and the gusset backing bar 46 toward one another inunison (by swinging the rods 49, 50) while the strips 11 are dwellingand by pressing the strips between the bars and simultaneously heatingthe strips with the bars. Heat is applied to the bars by electricheaters 51 (FIG. 6) which are embedded in the support blocks 47 and 48,the heat being conducted to the bars through the blocks.

To prevent the hot gusset sealing and backing bars 45 and 46 fromsticking to the outer faces of the strips 11, a protective curtain 52(FIGS. 4 and 5) of the same material as the curtain 41 is draped overthe splitter 28 adjacent the two bars and straddles the strips. As shownin FIG. 4, the curtain extends downwardly from the splitter to a levelbelow the bottomOon one panel of the curtain being sandwiched betweenthe gusset sealing bar and the front face of the gusset 17 while theother panel of the curtain is sandwiched between the backing bar and therear face of the gusset. As with the panels 31, the gusset is sealedthrough the curtain while the latter prevents direct contact of thesealing bars with the portion of the strips forming the gusset toprevent the bars from sticking to the gusset.

To enable vertical adjustment of the gusset sealing bar 45 and thegusset backing bar 46, the mounting blocks 47 and 48 are adjustablymounted on their respective pair of rods 49, 50 for sliding along therods. For this purpose, the rods are clamped between the back surfaces52 (FIG. 6) of the blocks and clamping plates 53. Each clamping plate ismounted on its respective block by a screw 54 which extends through thecenter of the plate, between the rods, and is threaded into the block.After each bar is positioned, each screw is turned to force itsrespective clamping plate toward its respective block thus clamping theblock on the respective rods.

If the common top datum line concept is employed and the packagingmachine is changed over to run strips 11 having a greater height thanthose shown in FIG. 5, it is necessary only to lower the gusset bars 45and 46 by sliding the blocks 47 and 48 downwardly on the rods 49 and 50.If the common bottom datum line concept is employed, no change in theelevation of the gusset bars is required when the packaging machine ischanged over to run strips of a greater height. Thus, like the upstreamsealing mechanism 33, only relatively simple adjustments, if any, needbe made to the gusset sealing mechanism 34 when the machine is changedover.

Herein, the rectangular sealing bar 35 and the rectangular backing bar36 may not always seal the area on the panels 31 directly above the topof the gusset 17. This is true because pressure is exerted on the panelsonly in the area where the bars engage the curtain 41, and the latteroften may not ex tend completely down to the top of the gusset. Toinsure that the rectangular seal 29 will be continuous from just belowthe splitter 28 to the top of the gusset, a secondary rectangularsealing bar 56 (FIG. 5) is carried on the front support block 47 abovethe gusset sealing bar 45 and a secondary rectangular backing bar 57(FIG. 7) is carried on the back support block 48 above the gussetbacking bar 46. As shown in FIG. 4, this arrangement results in anoverlap of the seal formed by the rectangular sealing bar 35 and theseal formed by the secondary rectangular sealing bar 56 and insures theformation of a complete seal 29 along the height of the panels 31.

Because the gusset 17 is four strips 11 thick while the area of thepanels 31 is only two strips thick, the spacing between the gussetsealing bar 45 and the gusset backing bar 46 must be greater duringsealing than the spacing between the secondary rectangular sealing bar56 and the secondary rectangular backing bar 57. In this instance, thegusset backing bar 46 and the secondary rectangular backing bar 57 areformed as an integral part of the back support block 48, and theirsealing faces lie in a common plane (see FIG. 7). As best shown in FIG.5, the sealing face of the gusset sealing bar 45 is closer to {the face58 of the front support block 47 than is the sealing.

face of the secondary rectangular sealing bar 56 thereby to provide thenecessary spacing difference during sealing. Herein, the secondaryrectangular sealing bar 56 is formed as an integral part of the frontsupport block 47.

In many instances, the same packaging machine may be used to make bags12 from strips 11 which vary in thickness from run-to-run. That is, themachine may be used to run a series of bags with strips of one thicknessfor a period of time and then changed over to run bags from strips of agreater or lesser thickness.

In accordance with another aspect of the invention, the sealing unit 10may be changed over to seal strips 11 which vary in thickness fromrun-to-run by making a simple adjustment to the gusset sealing bar 45and without the necessity of replacing a major component of the sealingunit. For this purpose, the gusset sealing bar is adjustably mounted onthe front support block 47 for movement laterally of the secondaryrectangular sealing bar 56 and laterally with respect to the sealingposition of primary rectangular sealing bar 35 and the path of thestrips. With this arrangement, the gusset sealing bar 45 can be adjustedto compensate for the change in relative thickness between the panels 31and the gusset 17 caused by the gusset being four strips thick and thepanels being only two strips thick thus insuring that both the gussetsealing bar 45 and the secondary rectangular sealing bar 56 will beeffective to press against and seal the strips.

When the thickness of the strips 11 is increased from one run to thenext, the spacing between the sealing faces of the gusset sealing bar 45and the gusset backing bar 46 in their sealing positions must beincreased a distance twice as great as the increase in spacing betweenthe sealing faces of the secondary rectangular sealing bar 56 and thesecondary backing bar 57 in their sealing positions. Likewise, whenthinner strips are run, the spacing between the gusset sealing andbacking bars 45 and 46 must be decreased a distance twice as great asthe decrease in spacing between the secondary rectangular sealing andbacking bars 56 and 57. These relative changes must be made so that thestrips will be pressed uniformly between the bars during sealing. Suchrelative changes in spacing are accomplished by adjusting the gussetsealing bar 45 laterally with respect to the secondary rectangularsealing bar 56. With the sealing faces of the gusset backing bar 46 andthe secondary rectangular backing bar 57 lying in the same plane, thelateral spacing between the sealing faces of the gusset sealing bar 45and the secondary rectangular sealing bar 56 should always be kept equalto the thickness of the two strips 11.

In this instance, the lateral spacing between the sealing faces of thebars 45 and 56 is made adjustable by mounting the gusset sealing bar 45releasably on the front support block 47 with two' screws 59 (FIG. 8)and by spacing the bar 45 from the block with a shim 60. When thethickness of the strips 11 is to be increased, the shim is replaced by athinner shim to keep the sealing faces of the gusset sealing bar 45 andthe secondary rectangular sealing bar 56 spaced two strip thicknessesapart. A thicker shim is used as a replacement when thinner strips areto be run.

It will be observed that the use of separate sealing mechanisms 33, 34for fonning the major portion of the rectangular seals 29 and the gussetseals 30 is particularly advantageous. This is true because, when thepackaging machine is changed over to run bags 12 of a greater or lesserheight,

. only very minor and inexpensive changes need to be made to the sealingmechanisms regardless of whether the top datum line concept or thebottom datum line concept is employed in the machine. The utilization ofthe protective curtain 41 between the panels 31 and the backing bar 35and between the panels 31 and the backing bar 36 and terminating shortof the gusset 17 is particularly advantageous because the curtain causesthe bars to seal only above the gusset while allowing the lower endportions of the bars to extend downwardly alongside the gusset. Anotheradvantageous feature is the mounting of the gusset sealing bar 45 foradjustment laterally of the secondary rectangular sealing bar 56 so thatthe sealing unit can be used to form bags from strips 11 which vary inthickness from run-to-run without replacing expensive major pans.

I claim as my invention:

1. A sealing unit for sealing together face-to-face strips of flexiblematerial having panels joined by a fold which is tucked inwardly to forma gusset of W-shaped cross section along the fold and adjacent thepanels, the strips being advanced along a predetermined path and thesealing unit being operable to seal the strips crosswise at spacedintervals, said sealing unit comprising a first sealer having a backerbar mounted adjacent one side of said path and extending crosswise ofsaid strips, a generally rectangular heat sealing bar located on theother side of said path opposite said backer bar and extending crosswiseof said strips, means disposed between said panels and said sealing barand tenninating short of said gusset to keep said sealing bar frompressably engaging said gusset while conducting heat from said sealingbar to said panels, and mechanism for periodically moving one of saidbars laterally of said path to press said panels against the other ofsaid bars to seal the panels together, said sealing unit also comprisinga second sealer spaced along said path from said first sealer, saidsecond sealer having backing means mounted adjacent one side of saidpath alongside said gusset and having a heated gusset seal bar mountedon the other side of said path opposite said backing means, andmechanism for periodically moving said gusset seal bar relative to saidbacking means and laterally of said path to press said gusset againstsaid backing means to form a gusset seal along the fold whereby thestrips are formed into a series of connected gusset bottom bags.

2. The sealing unit of claim 1 in which said means comprises a sheet ofheat conductive protective material having a thickness equal to orgreater than the thickness of an individual strip, said sheet beingbetween the strips and the sealing bar of said first sealer in aposition to cover the area of the panel opposite such bar while leavingthe gusset exposed.

3. A sealing unit as defined in claim 2 for sealing strips whose panelsmay, from run-to-run, vary in crosswise dimension within a predeterminedrange of dimensions, said bars of said first sealer being at least aslong as the panels of greatest crosswise dimension within said ran e,and said sheet being changeable to keep the sheet corre ated in lengthmm the crosswise dimension of the panels of the strips being sealedwhile leaving the gusset of such strips exposed.

4. The sealing unit of claim 1 in which said second sealer furtherincludes a secondary rectangular seal bar movable with and locatedadjacent said gusset seal bar, and said gusset seal bar being adjustablymounted for movement laterally of said path and relative to saidsecondary rectangular seal bar whereby said sealing unit may be adjustedto form bags from strips which, from run-to-run, may vary in thicknesswithin a predetermined range of thicknesses.

2. The sealing unit of claim 1 in which said means comprises a sheet ofheat conductive protective material having a thickness equal to orgreater than the thickness of an individual strip, said sheet beingbetween the strips and the sealing bar of said first sealer in aposition to cover the area of the panel opposite such bar while leavingthe gusset exposed.
 3. A sealing unit as defined in claim 2 for sealingstrips whose panels may, from run-to-run, vary in crosswise dimensionwithin a predetermined range of dimensions, said bars of said firstsealer being at least as long as the panels of greatest crosswisedimension within said range, and said sheet being changeable to keep thesheet correlated in length with the crosswise dimension of the panels ofthe strips being sealed while leaving the gusset of such strips exposed.4. The sealing unit of claim 1 in which said second sealer furtherincludes a secondary rectangular seal bar movable with and locatedadjacent said gusset seal bar, and said gusset seal bar being adjustablymounted for movement laterally of said path and relative to saidsecondary rectangular seal bar whereby said sealing unit may be adjustedto form bags from strips which, from run-to-run, may vary in thicknesswithin a predetermined range of thicknesses.